WO1996017477A1 - Method and apparatus for adaptive encoding/decoding - Google Patents

Method and apparatus for adaptive encoding/decoding Download PDF

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Publication number
WO1996017477A1
WO1996017477A1 PCT/US1995/012106 US9512106W WO9617477A1 WO 1996017477 A1 WO1996017477 A1 WO 1996017477A1 US 9512106 W US9512106 W US 9512106W WO 9617477 A1 WO9617477 A1 WO 9617477A1
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WO
WIPO (PCT)
Prior art keywords
entropy
quantized transform
transform coefficients
parameter set
parameter
Prior art date
Application number
PCT/US1995/012106
Other languages
English (en)
French (fr)
Inventor
Cheung Auyeung
Original Assignee
Motorola Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Priority to EP95935058A priority Critical patent/EP0742986A4/en
Priority to AU37223/95A priority patent/AU689658B2/en
Priority to CA002179408A priority patent/CA2179408C/en
Publication of WO1996017477A1 publication Critical patent/WO1996017477A1/en

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
    • H03M7/40—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code
    • H03M7/42—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code using table look-up for the coding or decoding process, e.g. using read-only memory
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/13—Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
    • H04N19/91—Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Definitions

  • the invention relates generally to the field of video compression, and in particular, to entropy coding.
  • Video systems are known to include a plurality of communication devices and communication channels, which provide the communication medium for the communication devices.
  • the communication channel may be wireline connections or radio frequency, RF, carriers.
  • video that needs to be communicated over the communication medium is digitally compressed.
  • Digital compression reduces the number of bits needed to represent the video while maintaining perceptual quality of the video. The reduction in bits allows more efficient use of channel bandwidth and reduces storage requirements.
  • each communication device may include an encoder and a decoder.
  • the encoder allows a communication device to compress video before transmission over a communication channel.
  • the decoder enables the communication device to receive compressed video from a communication channel and render it visible.
  • Communication devices that may use digital video compression include high definition television transmitters and receivers, cable television transmitters and receivers, video telephones, computers and portable radios.
  • FIG. 1 is a flow diagram of steps for one embodiment of a method for adaptive entropy encoding in accordance with the present invention.
  • FIG. 2 is a flow diagram of steps for one embodiment of a method for adaptive entropy decoding in accordance with the present invention.
  • FIG. 3 is a block diagram of one embodiment of an apparatus for adaptive entropy encoding/decoding in accordance with the present invention.
  • FIG. 4 is an exemplary prior art illustration of a method of scanning and transforming a two dimensional block to provide a one dimensional array of scanned coefficients.
  • FIG. 5 is a graphical depiction of the average power, in general, of the scanned coefficients with respect to the index; a distinction between lower and higher power coefficient is made in accordance with the present invention.
  • the present invention is a method and an apparatus for adaptive entropy encoding/decoding of a plurality of quantized transform coefficients in a video/image compression system.
  • For encoding first, a predetermined number of quantized transform coefficients are received in a predetermined order giving a generally decreasing average power. Then the quantized transform coefficients are parsed into a plurality of coefficient groups. When a last coefficient group comprises all zero quantized coefficients, the last coefficient group is discarded. The coefficient groups are then converted into a plurality of parameter sets in the predetermined order. A current parameter set is obtained from the parameter sets in the reverse order of the predetermined order.
  • a current entropy encoder is selected adaptively based on the previously selected entropy encoder and the previous parameter set. The current parameter set is encoded by the current entropy encoder to provide entropy encoded information bits.
  • This invention may be used with a compression algorithm that processes a picture into two-dimensional blocks of quantized transform coefficients with predetermined transform sizes. Each block is then scanned into a one-dimensional array in a predetermined order giving generally decreasing average power.
  • the one-dimensional array of quantized transform coefficients are parsed into a sequence of coefficient groups as shown by the following example. For example, consider an array having 64 coefficients, only five of which are non-zero:
  • the coefficient groups are ⁇ 0, 0, 1 ⁇ , ⁇ 0, -2 ⁇ , ⁇ 3 ⁇ , ⁇ 0,1 ⁇ , ⁇ 0, 0, 1 ⁇ .
  • the number of coefficient groups is the same as the number of non-zero coefficients since the last group ⁇ 0, 0, ... ⁇ , which consists of all zero coefficients, is discarded.
  • Each coefficient group has the form
  • r is the run, which may be equal to zero, defined as the number of zero coefficients in the coefficient group
  • 1 is the level
  • e is the end-of-block indicator which indicates whether the parameter set is the first set of the coefficient groups.
  • the parameter set is the first set of the coefficient groups
  • e is set to one
  • the parameter set is other than the first set of coefficient groups
  • e is set to zero.
  • the coefficient group ⁇ 0, 0, 1 ⁇ becomes the parameter set ⁇ 2, 1 , 1 ⁇
  • the coefficient group ⁇ 3 ⁇ becomes the parameter set ⁇ 0, 3, 0 ⁇ .
  • FIG. 1 is a flow diagram of steps for one embodiment of a method for adaptive entropy encoding in accordance with the present invention.
  • a plurality of quantized transform coefficients are scanned in a predetermined scanning order giving a generally decreasing average power and the plurality of quantized transform coefficients are stored in a memory unit.
  • the first step in the encoding method is parsing a predetermined number of quantized transform coefficients into a plurality of coefficient groups and converting the coefficient groups into a plurality of parameter sets according to a predetermined scheme and storing the parameter sets in the memory unit (102).
  • Each parameter set includes a level parameter which is a value of a non zero quantized transform coefficient.
  • the second step in the encoding method is accessing, from the memory unit, each parameter set of the plurality of parameter sets in a reverse order of the predetermined scanning order (104).
  • the third step in the encoding method is adaptively selecting a current entropy encoder of a plurality of entropy encoders based on a previous level parameter of a previous parameter set and a previously selected entropy encoder (106).
  • the fourth and final step in the encoding method is encoding, by the current entropy encoder, a current parameter set to provide entropy encoded information bits.
  • the parameter sets and stored in the memory unit in the form ⁇ r, 1, e ⁇ . The encoding process is repeated until the end-of-block parameter of the final parameter set indicates that the current parameter set is the last parameter set to be encoded.
  • FIG. 2, numeral 200 is a flow diagram of steps for one embodiment of a method for adaptive entropy decoding in accordance with the present invention.
  • the first step in the decoding method is decoding, by a current entropy decoder, the entropy encoded information bits to provide a decoded current parameter set (202).
  • the second step in the decoding method is adaptively selecting a next entropy decoder of a plurality of entropy decoders based on a decoded current level parameter of the decoded current parameter set and a previously selected entropy decoder (204).
  • the third step in the decoding method is storing, into the memory unit, each parameter set of a plurality of decoded parameter sets in the reverse order of the predetermined scanning order (206).
  • the fourth and final step in the decoding method is converting the decoded parameter sets into a number of decoded quantized transform coefficients according to the predetermined scheme in the predetermined scanning order and storing the decoded quantized transform coefficients in the memory unit (208). Where the number of decoded quantized transform coefficients is less then the predetermined number of quantized transform coefficients, zero- valued decoded quantized transform coefficients will be appended.
  • the decoding process is repeated until the end-of-block parameter of the current parameter set indicates that the current parameter set is the last parameter set to be decoded.
  • the current entropy encoder for encoding the current parameter set is adaptively chosen from a sequence of entropy encoders
  • the current entropy decoder for decoding the entropy encoded information bits is adaptively chosen from a sequence of entropy decoders corresponding to the sequence of entropy encoders.
  • the entropy encoders/decoders can be based on variable length codes or arithmetic codes. Let n>2, and El , E2, ...,En be a sequence of entropy encoders/decoders, and Ti , T2, ..., Tn-1 be the corresponding sequence of positive thresholds of increasing magnitude.
  • the sequence of entropy encoders/decoders is arranged in the order of ability to code increasing levels.
  • a more efficient coding scheme for a particular encoder/decoder is selected based on the information that the levels to be coded by the particular encoder/decoder do not exceed a corresponding threshold.
  • the adaptation is performed as follows.
  • Ei is used to encode/decode the first parameter set.
  • E -l be the entropy encoder/decoder used to encode/decode the previous parameter set, (r, 1, e). If ll I>T
  • FIG. 3 is a block diagram of an apparatus for adaptive entropy encoding/decoding in accordance with the present invention.
  • the apparatus comprises a first memory unit (302), a parameter set determiner (304), an order reverser (306), an encoder controller (308), and a plurality of entropy encoders (31 0).
  • the apparatus further comprises a plurality of entropy decoders (31 ), a decoder controller (314), a second memory unit (316), and a parameter set converter (318).
  • the quantized transform coefficients (320) are received and stored in the first memory unit (302).
  • the parameter set determiner (304) accesses the quantized coefficients in the memory unit (302).
  • the parameter set determiner (304) parses and converts the quantized transform coefficients (320) into a plurality of parameter sets (322) in a predetermined order of generally increasing average power and stores the parameter sets in the memory unit (302).
  • the order reverser (306) accesses the parameter sets (322) in the memory unit (302) in the reverse order of the predetermined order.
  • the order reverser (306) sends the level of the current parameter set (324) to the encoder controller (308).
  • the encoder controller (308) adaptively selects a current entropy encoder from the plurality of entropy encoder (310) based on the previous entropy encoder and the previous level. The encoder controller (308) then switches the current parameter set (326) to the current entropy encoder and switches the output of the current entropy encoder to form the entropy encoded information bits (328).
  • the decoder controller (314) switches the entropy encoded information bits (328) to the current entropy decoder in the plurality of entropy decoders (312).
  • the current entropy decoder decodes the entropy encoded information bits (328) and generates the current decoded parameter set (330).
  • the decoder controller (314) then adaptively selects the next entropy decoder from the plurality of entropy decoders (312), corresponding to the set of entropy encoders (310), based on the current entropy decoder and the current level of the current decoded parameter set (330).
  • the current parameter set (330) is stored in a second memory unit (316).
  • the parameter set converter (318) accesses the second memory unit (316) to convert the parameter sets back into quantized transform coefficients and store the quantized transform coefficients in the second memory unit (316).
  • the decoded quantized transform coefficients (332) are then output from the second memory unit (31 6),
  • the present invention is based on the observation that the quantized transform coefficients scanned in the order of decreasing average power have different amount of average power in different locations of the scan. Therefore different entropy encoders should be used adaptively to code the quantized transform coefficients in different location of the scan.
  • FIG. 4, numeral 400 is an exemplary prior art illustration of a method of scanning and transforming a two dimensional block to provide a one dimensional array of scanned coefficients.
  • a two- dimensional block of 64 quantized discrete cosine transform coefficients is illustrated by the two-dimensional grid (402) in increasing horizontal frequency (406) from left to right and in increasing vertical frequency (408) from top to bottom.
  • the quantized transform coefficients are scanned in a zig-zag order (404) as described in the MPEG-1 and H.261 standard to form a one- dimensional array of 64 quantized coefficients.
  • FIG. 5, numeral 500 is a graphical depiction of the average power, in general, of the scanned coefficients, where the graph of the average power of the scanned coefficients is separated into higher (506) and lower (508) power coefficient groupings.
  • a distinction between lower and higher power coefficient is made in accordance with the present invention.
  • the average power (502) of the zig-zag scanned coefficients in 400 decreases as a function of its index (504).
  • the index is defined as the order in which a coefficient was scanned.
  • the zig-zag scanned coefficient are divided into the higher power coefficients (506), and the lower power coefficients (508) by a threshold (51 0). Because of different statistical properties of the higher power coefficients (506) and the lower power coefficients (508), one entropy encoder is used to code the higher power coefficients (506), and another entropy encoder is used to code the lower power coefficients (508).
  • the present invention codes the quantized transform coefficients with less number of bits than the coding method used in MPEG-1 , MPEG-2, and H.261 .
  • the present invention adapts to each block of quantized transform coefficients while the coding method in MPEG-1 , MPEG-2, and H.261 does not.

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)
  • Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
  • Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
PCT/US1995/012106 1994-12-01 1995-09-25 Method and apparatus for adaptive encoding/decoding WO1996017477A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP95935058A EP0742986A4 (en) 1994-12-01 1995-09-25 METHOD AND DEVICE FOR ADAPTIVE ENCODING / DECODING
AU37223/95A AU689658B2 (en) 1994-12-01 1995-09-25 Method and apparatus for adaptive encoding/decoding
CA002179408A CA2179408C (en) 1994-12-01 1995-09-25 Method and apparatus for adaptive encoding/decoding

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/347,639 1994-12-01
US08/347,639 US5473376A (en) 1994-12-01 1994-12-01 Method and apparatus for adaptive entropy encoding/decoding of quantized transform coefficients in a video compression system

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WO1996017477A1 true WO1996017477A1 (en) 1996-06-06

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US (1) US5473376A (zh)
EP (1) EP0742986A4 (zh)
CN (1) CN1140003A (zh)
AU (1) AU689658B2 (zh)
CA (1) CA2179408C (zh)
WO (1) WO1996017477A1 (zh)

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Also Published As

Publication number Publication date
CA2179408C (en) 2000-06-06
EP0742986A4 (en) 2000-12-13
US5473376A (en) 1995-12-05
AU689658B2 (en) 1998-04-02
AU3722395A (en) 1996-06-19
EP0742986A1 (en) 1996-11-20
CA2179408A1 (en) 1996-06-06
CN1140003A (zh) 1997-01-08

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